Systematic and ecological studies of the Diatom Flora of the coastal waters Alexandria

Abstract

The investigated area, the Eastern Harbour of Alexandria, is a semiclosed basin, except on its northern side where it communicates with the sea through two outlets. It is about 11 m in average depth and 6 km in greater width. Four sampling station were chosen to represent sites of different exposure to pollution. The samples have been taken throughout 13 months with 16 sampling trip from August 1989 to August 1990. The sampling trips as more frequent during August - September 1989. Surface temperature ranged between two extremes, 16.1 C° in January and 29.2 C° in August with a small decreasing vertical gradient. Surface salinity fluctuated in a relatively wide range from 36.1%. to 39.06%. with a higher minimum and maximum in the subsurface layers (2 m and 5 m). Thigher salinities were recorded twice. Once from end of September to November 1989 and again secod in March through July 1990. The vertical gradient of o, is more pronounced from 0.5 to 5 m than from 0.5 m to 2 m. The surface o, fluctuated between 23.23 to 27.97, and from 25.34 to 28.71 at 5 m. The secchi disc transparency showed wide variations, from 0.5m to 5m occasionally reaching down to the bottom at the marginal shallow stations. The surface layer was supersaturated with oxygen all over the Eastern Harbour. Throughout the year except for September (1 and 4) and December (Station 1). There is a decreasing